Chas Cloth MRQ Temporal AA Render + Chaos Cloth Kinematic Collider issues

Development Asset Creation
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This question was created in reference to: [Chaos Cloth Physics Asset MRQ Temporal AA [Content removed]

Hi!

We are continue to facing the same issue described in the referenced linked question above that appears at 5.5.4 and one more issue discovered.

So currently we are jumped up to Unreal Engine 5.6 and here is a two issues that we facing:

  1. The first one is linked to the issue that we faced before in 5.5. version of the engine. When we are using a chaos cloth asset with simulation, when rendering with Temporal AA with 13-17 samples (the count matter, more subsemples more blur and smudges at render). So the simulation appears at every render substep, which leads to super blur and smudged result at the end render. The SpatialAA looks fine, because there is no any substeps for render, but in that case no motion blur on render at all. As we discussed before there should be a fix for that issue, but looks like it doesnt work.
  2. When we using a kinetic collider option in the chaos asset assembly - the cloth overlaps with underliying skeletal mesh that used as collider. Any animation cause an overlaps with simulation. We spent a lot of time trying to find the issue. And we took the Epic’s Talisman project called Captain Eli with the chaos cloth asset for lookdev tests. And here is what we figured out: when using UE 54 all kinematic collisons works fine. But when we transferred project to UE 56 - it immidiatly shows up the overlaps. See the videos attached.

So the main question is:

  1. Do we have ability to render chaos cloth simulation with Temporal AA with correct motion blur and simulation that doesnt made a calculations everysubstep. I dont know, but is there a way to keep the simulation and have a motion blur? We thought that your fix should be implemented and resolve that issue.
  2. What happens with the kinematic collider? Why there are overlaps?

We will provide you with our test project where you can find the asset and you can lookdev it. You can also take a llok for the Talisman Project - CapEli - look at her hands in 5.6

Upd. We also find the issue, where the chaos cloth asset is not rendering in a viewport, after project restarts.

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Steps to Reproduce

  1. Create a Chaos Cloth Asset and import necessary loth files.
  2. Set up the kinematic collider and physics options. Insert the any animation for the preview window. Tou can see the overlaps with the cloth asset and the underlying skeletal mesh that used as collider.
  3. Implement the chao cloth asset into character’s BP with the skeletal mesh as a parent component.
  4. Set up the sequencer, camera and render it with MRQ with a Temporal AA 12-17 samples.
  5. See how cloth simulation appears at every subframe.
  6. Check the render result - all cloth simulation are bluried.

Or:

  1. Open the delivered project, the map with asset will load automatically
  2. In the Content folder start the LS_ChaosCFX_Test_v03 sequence
  3. Press simulatebutton and start the sequence play - you can see overlaps with the kinetic collider active
  4. Render the sequence with the TemporalAA with 13-17 samples - you can see how the simulation continues with the every subframe.
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I also want to attach screencast on how chaos cloth sim looks with temporal AA Rendering:

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My team is also experiencing the kinematic collider overlap/clipping you described in our project after upgrading to UE 5.6.

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Hi [mention removed]​ [mention removed]​ !

Could you please take a look at this issue?

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Morning Andrei,

The dev side are going to take a look into the kinematic collider issue - it seems to be transient in that if I play back frame by frame it will resettle correctly, but will penetrate during playback.

On the temporal AA side, this is an interesting one which very rarely comes up outside of virtual production - the advice I had from the MRQ team was to cache and playback. I think that is still the recommended way, but I’m wondering this morning if we could try another way.

The temporal AA doesn’t work with simulation on the high frequency of samples because the physics only simulates in ‘chunks’ of time - and this system effectively bumps up the frame rate to a huge number (ie you end up with a simulation sequence of 0 sim steps for a while, then 1 step, then 0 steps etc) . The cache and playback method solves this because it can LERP between these steps.

When you mention above that the recommended way isn’t working, can you provide some further detail please?

Thanks!

Geoff

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Like Geoff said, the only way to make temporal AA work with cloth is to cache the simulation first.

As for the kinematic collider, I refactored it (it’s actually on a deprecation path for 5.7 in favor of Skinned Triangle Mesh physics asset collision bodies), so it looks like there has been a regression.

I can try to take a look at the example and see if there’s a workaround in the meantime.

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OK so I’ve figured out the bug, and I can put together a fix in 5.7 and also link the github change if you want to get it sooner.

The workaround is to upgrade to using the Skinned Triangle Mesh. Unfortunately, there is also a bug in 5.6 for it where the ClothCollisionThickness is not respected and always treated as 0, so you will need to increase the CollisionThickness instead. If you’re only using Kinematic Collider and not using any traditional Physics Assets, and your SelfCollisionThickness was constant (no weight map) it will be possible to just set CollisionThickness = SelfCollisionThickness + SelfCollisionKinematicColliderThickness. However, with the ClothCollisionThickness bug, it will not be possible to upgrade Kinematic Colliders with weight map SelfCollisionThickness.

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Ok! Many thanks for clarification. I hope you can release a fix in github soon.

And also thanks for advise for using cache.

One more note for using cache - if we will use a high dencity cloth asset, which took a time for simulation calculations, with the fast and impulse animation, we will have a issues while recording the cache, like lags and unpredictable cloth behavior. Any advise on this? M first thoughts is to slowdown the sequence at least twice for chaos caching, after that - go norm speed again.

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Hi [mention removed]​

Could you please clarify when will you able to submit a fix to github?

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[mention removed]​ [mention removed]​ Hi guys! Any chance to get the fix in code update?

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Sorry, we were on summer break, but the fix is here: https://github.com/EpicGames/UnrealEngine/commit/3f4911c8e4a86fa511d23ac5244c8f846ab918bd